Evaluation of pervious concrete as a best management practice for stormwater in Edwards Aquifer region

Rapid urbanization and land development activities in San Antonio and Austin-San Antonio corridor is a huge concern for the runoff quantity and water quality of the Edwards Aquifer, which is the only source of drinking water supply for the people of this region. Thus, to preserve the natural quality and quantity of recharge the maximum impervious cover in any type of land development within the recharge zone has been restricted by regulations. As indicated in 30 Texas Administrative Code Chapter 213, if a development requires greater than 20% impervious cover, a permanent stormwater best management practice (BMP) must be constructed to ensure that no dilapidation of stormwater quality is created by the development.

Use of pervious concrete in sidewalks and parking lots is among the BMPs recommended by the EPA and included as a permanent BMP in the TCEQ Technical Guidance Manual (TGM) for using in Edwards Aquifer. However, the use of this BMP is very limited in Edwards Aquifer area because of the lack of knowledge and experience. Moreover, no standard mix-design for pervious concrete has been recommended in the TGM.

In this study, pervious concrete has been studied as a BMP in the Edwards aquifer region. A guideline for the mix-design of pervious concrete is developed, which would optimize the porosity, strength, and pollutant removal capacity to serve its purpose in the Edwards Aquifer zone. The study suggests that the porosity and hydraulic conductivity can be increased by decreasing the proportion of fines (sand) in concrete. The consequence of decreasing the proportion of fines is the loss of strength. Thus, an optimization is proposed to maximize the strength and porosity for infiltration.

A high porosity and permeability of the pervious concrete is not the only property that controls the amount of recharge. The limiting factor of net recharge is often depends on the permeability of the subgrade soil. This study also suggests that a higher porosity might decrease the removal capacity of metals and suspended solids of pervious concrete. Thus, the optimization might be site specific and must consider the hydraulic conductivity of the subgrade soil, strength, pollutant removal capacity, and infiltration capacity of the pervious concrete.